Current automatic power transmissions generally include a hydrodynamic input device such as a torque converter or fluid coupler. A torque converter is employed mainly to provide torque multiplication in the lower speed range. A torque converter consists of an engine-driven impeller, a fluid turbine, and a fluid stator. The engine-driven impeller accelerates fluid for passage to the turbine. The turbine converts the fluid energy coming from the impeller into mechanical energy, which is transmitted to the input shaft of a transmission.
The stator mechanism disposed between the fluid inlet of the impeller and the fluid outlet of the turbine redirects the fluid from the turbine to the impeller thereby improving the flow efficiency and increasing the torque multiplication of the hydrodynamic torque converter. The fluid passes from the inner section of the impeller torus substantially radially outward in a toric path and then through the path in the turbine in a substantially toric path back to the stator. In constant area turbine assemblies, the flow therein can encounter energy losses when a reversal or separation in flow occurs near the center of the torus flow path adjacent the inner side wall. This flow inconsistency reduces the efficiency of the torque converter.
A stator is made up of a plurality of stator blades, which are connected at one end to a relatively small ring, the shell, and at the other end to a larger ring, the core. Fluid flowing through the stator passes along the stator blades. These blades force the fluid to change direction so fluid exiting the stator enters the pump flowing in the same direction as the pump is rotating, thereby conserving power. Stator blades with a larger surface area are more effective at re-directing the fluid. The core has conventionally limited the surface area of the stator blades because the sides of a standard stator blade are linearly configured between the core and the shell. This design often results in a stator blade with a relatively small surface area, and therefore a loss of potential torque.
The stator blade cross-sectional design is important in the overall design of a torque converter. Stator blade shapes that result in flatter input speed lines allow for engine operation at lower engine speeds, which improves vehicle fuel economy. Additionally, flatter input speed lines improve performance in some vehicle applications due to smaller changes in engine speed when the torque converter clutch is applied.
An example of a conventional torque converter assembly is described in U.S. Pat. No. 4,177,885 and an example of a conventional torque converter stator is described in U.S. Pat. No. 5,431,536, both of which are assigned to General Motors Corporation and are hereby incorporated by reference.